6 Journal of Co}}iparative Neurology and Psychology. 



in (see below) is t,nven under A + S, (axis + sheath), the total 

 diameter of each fiber, while under A (axis) is t^iven the diame- 

 ter of the axis. The two columns to the ri_<j;ht i^ive the corre - 

 spondint^ radii. The measurements were first put down in 

 terms of the divisions of the ocular micrometer — the subdivis- 

 ions being estimated to tenths of these units. 



'I'Aiu.i'; III. 



Diameters ami llidii of entire nb;;r.s and axes, in ilivisioiis of 

 the (xuhir micrometer. 



To transform these measurements into // we multiply in 

 each instance by the value of one division of the ocular micro- 

 meter which in this case was 3.06 /i. As the radii alone will 

 be used, they only are reduced to //. (See Table IV.) 



It is on the basis of these radii that we calculate the areas 

 of the fibers and of their axes, and for this we employ the 

 formula tt?* giving tt the value of 3. 14. 



As the square of the average radius for the grt)up is not 

 equivalent to the average of the squares of the radii, and as the 



